1. Field of the Invention
The present invention relates to a semiconductor manufacturing apparatus and method for manufacturing semiconductor elements, display elements, and the like and, more particularly, to a semiconductor manufacturing apparatus which comprises a mechanism for automatically cleaning foreign matter attached to the rear surface of a wafer, and a semiconductor manufacturing method.
2. Related Background Art
A conventional exposure apparatus used in the manufacture of semiconductor elements, liquid crystal display elements, and the like has a substrate stage, and a substrate holder which is placed on the substrate stage and holds a photosensitive substrate (a wafer, glass substrate, or the like). The substrate holder has a vacuum chuck groove on its surface so as to immovably hold a substrate upon transfer of a pattern image on a mask onto the substrate. By reducing the pressure in the gap between the vacuum (reduced pressure) chuck groove on the substrate holder surface and the substrate, the substrate holder chucks or holds the rear surface of the substrate by vacuum suction.
Upon reduction of the pressure (vacuum suction) when the substrate holder chucks the substrate, if foreign matter (a fine particle as small as about 1 .mu.m) becomes attached to the rear surface of the substrate, the flatness of the exposure surface (front surface) of the substrate is impaired due to the influence of the foreign matter. The impaired flatness of the exposure surface causes a displacement error or a focus error in each shot area on the substrate, and seriously deteriorates the yield in the manufacturing processes of semiconductor elements and liquid crystal displays.
Conventionally, in order to prevent attachment of foreign matter, the rear surface of the substrate is washed in a pre-process, or the ratio of the contact area between the substrate holder and the substrate to the entire area of the substrate, i.e., the contact area ratio is reduced to about 6 to 7%.
However, in order to meet recent requirements for miniaturizing exposure patterns, the N.A. (numerical aperture) of an optical system (projection optical system) for transferring a pattern on a mask onto a substrate has increased, and the focal depth of the projection optical system has become increasingly small.
As the pattern is miniaturized, the allowable value of the displacement error also becomes small. Therefore, the allowable value of the size of foreign matter attached to the rear surface of the substrate becomes small upon miniaturization of exposure patterns.
Even when the rear surface of a substrate is washed in the pre-process, dust may be raised upon contact between a holding arm or the like of a conveying device and the rear surface of a wafer 1 during the conveyance of the substrate onto the substrate holder in the exposure apparatus, and foreign matter may become attached to the substrate.
The contact region of the rear surface of a wafer in the conventional exposure apparatus, and the influence of attached foreign matter will be explained below with reference to FIGS. 6A and 6B.
FIG. 6A shows a contact surface shape between a conventional wafer holder 2 and a wafer 1.
The wafer holder 2 has a plurality of contact regions contacting the wafer 1. The contact regions include a plurality of annular regions.
More specifically, the wafer holder 2 contacts the wafer 1 via contact regions (circular contact regions) 52 to 57 (solid circle regions in FIG. 6A) in FIG. 6A.
By reducing the pressures in the gaps defined between the wafer 1 and a region between the contact regions 52 and 53, a region between the contact regions 54 and 55, and a region between the contact regions 56 and 57, the wafer 1 is vacuum-chucked to the wafer holder 2.
Although the wafer 1 is not vacuum-chucked to the wafer holder 2 in other regions, grooves (e.g., between the contact regions 53 and 54) are formed on such regions to reduce the contact area between the wafer 1 and the wafer holder 2.
For example, as shown in FIG. 6B, when foreign matter (foreign matter 58 in FIG. 6B) is attached between the contact regions of the wafer 1 and the wafer holder 2, the flatness of the wafer 1 is impaired. On the other hand, when foreign matter (foreign matter 59 in FIG. 6B) is attached between regions where the wafer 1 and the wafer holder 2 do not contact, it does not influence the flatness of the wafer 1.